Regulation of skin blood flow in man is accompanied by both reflex and local mechanisms. Neural control derives not only from thermoregulatory reflexes, but also from non-thermoregulatory reflexes, such as those associated with exercise and blood pressure regulation. Local mechanisms include an important component associated with the level of local skin temperature at the site of blood flow measurement. This project is a continuation of our exploration into the regulation of this regional circulation when these sources of control are in competition with each other or are acting in concert. Major emphasis will continue to be placed on the regulation of skin blood flow during exercise, in which there is a built-in competition between thermoregulatory and non-thermoregulatory reflexes. Specific questions addressed in this proposal include (a) does the response of skin blood flow or of sweat rate to exercise depend more strongly on the muscle mass involved in the exercise, the specific muscle group, or on the mode of exercise (isometric versus dynamic)? (b) is the response of the cutaneous vasculature to the onset and continuation of dynamic or isometric exercise dependent on the level of exercise? (c) can a maximal skin blood flow be defined? (d) can the arterial occlusion at the wrist in venous occlusion plethysmography be replaced by wrist venous occlusion? (e) can the potent cutaneous vasoconstrictor response to the diving reflex in man be attenuated or abolished by local or whole body hyperthermia? (f) Do laser-doppler measurements of skin blood flow adequately follow plethysmographic measurements when the skin is vasoconstricted? Answers to these questions will substantially extend our knowledge regarding the control of this circulation and should set the stage for understanding how such control is modified in disease states as well as offer a rationale by which to assess the impact and risk of heat stress and exercise of patients with cardiovascular disease.